Nowadays, it is desired to manufacture aircraft using composite materials, in particular because of their reduced weight and because of their mechanical properties. Such composite materials are constituted by a matrix of synthetic material, e.g. epoxy resin, having embedded therein fibers such as carbon fibers.
When such a material is to be used in building an aircraft, it is useful to know how it behaves in terms of electrical resistance. For this purpose, the following procedure is nowadays implemented. A bar of composite material is made that comprises a stack of a plurality of plies. The number of plies is known and the plies are oriented, e.g. in the sequence 450/0°/−45°/90° . . . . A metal that is a good conductor of electricity is deposited electrolytically at both ends of the bar. A voltmeter is used to measure the potential difference that exists between those two deposits while the bar is being supplied with an electric current in series via an ammeter. Knowing the voltage and the current thus makes it possible to obtain the resistance of the bar in application of Ohm's law R=U/I.
Nevertheless, it is found to be relatively difficult to make the electrolytic deposit at the ends of the bar. Such an operation is lengthy, onerous, and without any guarantee of reliability. In particular, the quality of the surface treatment constituted by the electrolytic deposit depends to a large extent on the care applied in preparing the bar, which in practice means that it is necessary to implement about ten different steps in order to ensure that the deposit is made correctly. These steps call on specific personnel and means, thereby causing this service itself to present a cost that is not negligible. Furthermore, it is sometimes found that the results obtained are incoherent and depend in fact on the quality of the deposit that has been made. In addition, given that current is fed to the ends of the bar and that voltage is measured by means of clips, the electrolytic deposit ages quickly, which sometimes makes the experiment difficult to repeat.